184 Trails. Acad. Sci. of St. Louis. 



abruptly bent upward and swollen to form a circle of nodes 

 at the lower margin of the calyx. Surface of the calyx finely 

 granulose and convex enough to bring out the suture lines. 

 Anal area almost flat. — Geological formation. Upper Bur- 

 lington. 



Agaricocrinus Coreyi, Lyon and Casseday. 



All plates of the body tumid with abruptly raised trans- 

 verse ridges on each plate. Surface smooth. Anal area an 

 elongate distinctly rounded area, composed of small, smooth, 

 irregular pieces. — Geological formation. Keokuk. 



Agaricocrinus Wortheni, Hall. 



Plates within the concavity perfectly flat, others slightly 

 convex. Orals and radial dome plates large with rounded 

 nodes. Intervening pieces small and only slightly convex. 

 Surface finely granulo-striate. Anal area perfectly flat. 

 There is no anal ridge, the plates of the posterior area grow- 

 ing smaller as they approach the anus. — Geological forma- 

 tion. Keokuk. 



Agaricocrinus (Amphoracrinus) Americanus, Roemer. 



Plates within the concavity flat or slightly convex, while 

 the others are more or less convex and sometimes covered 

 with indistinct transverse angularities. Plates of the ventral 

 side highly convex, except the interambulacral pieces which 

 are much smaller and almost flat. Orals and radial dome 

 plates large and tuberculose. Surface granular or granulose 

 striate toward the margin of the plates. Anal area abruptly 

 protruding, formed into a large anal process with a broad de- 

 pression on either side. — Geological formation. Upper 

 Burlington and Keokuk. 



EXPLANATION OF ILLUSTRATIONS. 



Plates XVIIl-XXI. 



All the figures are drawings, by the author, of the ventral side of Agari- 

 cocrinus Americanus, and show the great variations in the number and dis- 

 tribution of the arms, and in the plates of the tegraen. All the drawings 

 are about natural size and drawn as if the arm bases had been flattened 

 out, regardless of perspective. 



Issued May 30, 1900. 



